1. Field of the Invention
The present invention relates to a flat panel display and, more particularly, to a double-sided organic light emitting device capable of preventing definition of image quality from being deteriorated by external light.
2. Description of the Related Art
Flat panel displays such as organic light emitting devices, field emission displays (FEDs) and so forth are subjected to considerable decrease in contrast according to intensity of external light. To prevent this phenomenon, for example, a black matrix for blocking external light has been used. In spite of using such a black matrix, it is very difficult to completely block the external light on an emission region to make a black state.
Meanwhile, such an organic light emitting device for blocking the external light using a circular-polarizing plate is disclosed in U.S. Pat. No. 5,596,246. The conventional organic light emitting device using the circular-polarizing plate is provided with an organic electroluminescent (EL) element consisting of a transparent electrode, an organic emission layer and a reflective electrode formed on an insulating substrate. The insulating substrate is encapsulated with an encapsulating substrate using a sealant (not shown in the drawing), and a circular-polarizing plate consisting of a linear-polarizing plate and a λ/4 compensating plate disposed on an outer surface of the insulating substrate.
The conventional organic light emitting device constructed as set forth above is designed so that an angle between a retardation axis of the λ/4 compensating plate and a polarization axis of the linear-polarizing plate becomes 45 degrees. Thus, the external light passes through the linear-polarizing plate to become linear-polarized light, and the linear-polarized light passes through the λ/4 compensating plate to become circular-polarized light. The circular-polarized light is reflected through the reflective electrode, and become linear-polarized light through the λ/4 compensating plate. The linear-polarized light is absorbed and blocked through the linear-polarizing plate. The conventional organic light emitting device as above-mentioned has an advantage in that it can improve contrast by blocking the external light using the circular-polarizing plate, but has a disadvantage in that it requires a separate reflective plate in order to block the external light.